A great number of products are packaged, by their manufacturers, for shipping and distribution in corrugated paperboard cartons or boxes. These corrugated paperboard boxes or cartons are typically supplied to their end user; i.e. the manufacturer of the products to be boxed and shipped, in a non-erected configuration. Clearly, it is not efficient to ship or transport fully set up or erected empty paperboard boxes from the box manufacturer to a product manufacturer, who will then fill these erected corrugated paperboard cartons with his product. Rather, these corrugated paperboard cartons are shipped to the end user in a non-erected configuration. The corrugated paperboard boxes arrive at the end user's facility each folded flat as a sleeve. Each carton's bottom and top flaps are usually then folded into place and glued or taped to complete the erection of the cartons immediately before their usage. These non-erected boxes are supplied to the end user by a corrugated box manufacturer.
The corrugated box manufacturer starts with a stack of sheets of corrugated paperboard which he obtains from a supplier of corrugated sheets. The overall size of each sheet has been determined by the box manufacturer or by the end user in accordance with the size of the intended corrugated box or carton. The corrugated paperboard sheets are received by the corrugated box manufacturer from the corrugated sheet supplier typically already provided with cross-corrugation score lines. These score lines will, when combined with score lines added by the corrugated box manufacturer, define lines of fold that will typically cooperate with slots cut into the corrugated sheets by the box manufacturer. In some situations, the corrugated sheets received from the supplier are not scored. In those instances, the box manufacturer must score, slot and print the corrugated sheets.
The corrugated sheets are slotted to create the carton's side panels and end flaps, and may also be printed with suitable graphics, as determined by the end user. A machine, typically referred to as a printer-slotter is used for this purpose. The printer-slotter is akin to a rotary printing press and includes one or more printing cylinders with the number of printing cylinders being equal to the number of colors that can be printed. The printer-slotter also is provided with multiple pairs of cooperating scoring heads and slotting knives.
Once the corrugated sheets have been scored, typically with the scores being arranged extending in a direction of travel of the corrugated sheets through the printer-slotter, they are forwarded along to slotting rollers which include a stitch tab cutting device that is configured with stitch tab cutting die blocks mounted on an upper male slotter head and which cooperate with a lower die cutting anvil. When a typical box blank is formed into a sleeve, at least one of its side edges is configured with a stitch tab. This stitch tab is an elongated flap on one of the side edges of the box blank, intermediate its leading and trailing edges, which stitch tab receives a suitable glue or adhesive prior to the box blank being folded about one of the previously formed, longitudinally extending score lines. Once the box blank has been so folded, to form a sleeve, the stitch or glue tab is utilized to join the side edges of the corrugated paperboard box blank together.
Leading and trailing stitch tab scraps are the portions of the corrugated paperboard box blank which are separated from the scored and slotted box blank during the passage of the scored and slotted box blank between the pair of stitch tab die cutting blocks and the cooperating lower die cutting anvil. Such stitch tab die cutting blocks and lower die cutting anvil devices are generally well known in the art. A stitch tab cutting die block is carried on the outer edge of the upper male slotter head with the stitch tab cutting knife portion of the die block being oriented generally transversely to the direction of box blank travel. Both leading and trailing edge stitch tab die cutting blocks are usually carried by the same upper male slotter head. Their spacing along the circumference of the upper male slotter head is adjustable in accordance with the length of the particular corrugated paperboard box blanks on which they are operating.
The cooperating lower die cutting anvil has a resilient upper surface into which the cutting edge of the stitch tab die cutting knives will be pushed as the die cutting block and the lower die cutting anvil roll on and off each other. The stitch tab scraps are cut from the slotted box blank as the box blank passes through the nip point defined by the stitch tab die cutting knife and the surface of the lower die cutting anvil.
In operation, the leading and trailing stitch tab scraps are supposed to be completely severed from the scored and slotted paperboard box blanks by the action of the stitch tab die cutting knife cooperating with the lower die cutting anvil. The now separated stitch tab scraps are ejected forwardly, in the direction of travel of the box blanks by the continued counter-rotation of the cooperating stitch tab die cutting blocks and lower die cutting anvil. The cutting knives are set in the die blocks at a slight angle with respect to a line that is transverse to the direction of box blank travel. This provides a properly shaped stitch tab. It also is intended to cause the severed stitch tab scraps to be ejected forwardly and to the side of the cooperating stitch tab die cutting block and lower die cutting anvil. Such an ejection to the side is intended to reduce the possibility of the stitch tab scraps being sandwiched between the now scored, slotted and cut box blanks.
What, in theory, always happens, under actual production conditions, often does not happen. Specifically, the stitch tab scraps that have been cut from the box blanks, by operation of the stitch tab die cutting blocks and the cooperating lower die cutting anvil, are not ejected properly. There are several reasons that the ejection does not occur. The primary one is an incomplete cutting of the stitch tab scraps from the box blank. This frequently occurs because the transverse stitch tab cutting knife is not properly located and does not cut across the stitch tab all the way to the stitch tab slot. Alternatively, the cutting knife may have a dull area and does not effect a clean cut, but instead merely compresses a portion of the box blank along the cut line. The depth of cut of the cutting knife may be set incorrectly or the cutting knife may shift during production. The resilient surface of the lower die cutting anvil may be irregular due to prolonged usage and may not cooperate with the knife of the cutting die to define a proper cutting point.
Whatever the cause, the result is that the stitch tab scrap is not cleanly severed from the leading and/or trailing edge of the box blank. This results in the retention of the stitch tab scraps with the box blank as it is further processed in anticipation of these blanks being either formed into sleeves, by use of the stitch tab, or being sent on to the ultimate user unjoined. The inclusion of these non-stripped or non-ejected stitch tab scraps in the otherwise finished product prepared by the box blank manufacturer is not acceptable. It results in a product that cannot be properly stacked and handled by automatic machines. It also results in a product that is not truly finished.
Various stitch tab stripping devices are generally known in the industry. They are typically in the form of attachments to the die cutting block or slotter head and require a separate attachment operation, as well as modification of the slotter head. They thus add a separate assembly which must be aligned and coordinated with the die cutting blocks so that the stitch tab scraps will be stripped and ejected. They also tend to utilize pins that pass into the stitch tab scraps and that then require further stripper plates, or the like, to separate the stitch tab scraps from the pins. In use, these prior art stitch tab stripping devices have not met with a great deal of commercial success. They are often too complicated, require modifications to the die cutting blocks, do not function properly and simply do not perform in a dependable, repeatable manner to separate the stitch tab scraps from the blanks.
In view of these shortcomings of the available devices, there is a need in the industry for a stitch tab scrap stripper that will operate properly. The leading and trailing edge stitch tab strippers, in accordance with the present invention fill that need. They are a substantial improvement over the prior art.